The present invention relates generally to hazardous waste, and, more specifically, to mercury removal from contaminated sites.
One form of hazardous waste is mercury. Large amounts of such waste have been generated in both military and civilian applications. Elevated levels of elemental mercury at various geographic locations are considered hazardous to the environment and within the regulatory provisions of the Environmental Protection Agency (EPA) of the U.S. Government.
Regulatory provisions require that mercury contaminated waste containing less than 260 parts-per-million be suitably treated to stabilize the mercury and prevent its leaching into the environment. The regulations include a Toxicity Characteristic Leaching Procedure (TCLP) which determines whether or not the mercury contaminated waste has been sufficiently stabilized for long term disposal without unacceptable leaching.
The stabilization and disposition of the mercury contaminated waste has been the subject of considerable investigation over many years for achieving an economically viable solution thereof. The problem of mercury contamination includes large geographic areas and enormous volumes of waste in the form of soil, sediment, dredge spoils, sludge, and other industrial wastes.
One effective manner for stabilizing mercury waste is the direct reaction of elemental mercury (Hg) with elemental sulfur (S) or sulfur compounds to form mercury sulfide (HgS). Mercury sulfide is a stable and insoluble compound, and substantially reduces its hazardous affects and leaching capabilities.
However, variously known processes for treating mercury contamination have different advantages and disadvantages, with high cost being a substantial disadvantage. In view of the large volume of mercury contaminated waste, the cost for mercury treatment must be sufficiently low to render economically feasible the treatment of the large volumes thereof.
In U.S. Pat. No. 6,399,849 an improved method for treating mercury containing waste is disclosed. Commercially available sulfur polymer cement (SPC) is used to stabilize the mercury in the waste, and is relatively inexpensive. However, the mixture of the stabilized mercury and waste is effected ex situ, and must then undergo a heating and melting process and subsequent cooling to form a monolithic or encapsulated final waste form for meeting the EPA leaching standards. In view of the large volume of mercury contaminated waste and the need for encapsulation thereof, this process has practical and economical limits.
Accordingly, it is desired to provide an improved method for treating mercury contaminated waste for reducing the cost thereof.